Improved process for the manufacture of chlorinated rubber



United States Patent i nwrnovnnr PROCESS FGR'EMANUFACTURE 1 6 Claims. --(c1. 260 772 This invention relates to an improved method for 'producing chlorinated rubber.

It is well known, of course, that rubber can be transformed into chlorinated derivatives thereof'by treatment 7 of rubber with chlorine under various conditions, the chlorination usually being carried out in a suitable solvent for rubber such as carbon tetrachloride orsimilar solvent which does-not react with the'chlorine. When'raw or crude rubber is chlorinated, a product is obtained having a very highviscosity, and, therefore, not economical to employ forthe preparation of lacquers, varnishes, inks,

and the like, requiring a low viscosity chlorinated rubber i to be practical. Accordingly, an importantproblemconfronting the art has been, and continues to be, an economical and practical method for producing low viscosity chlorinated rubber. Heretofore, various methods have been 1 proposed for accomplishing this objective, but they have all been deficient for various reasons.

More specifically; it; has been proposed to produce chlo rinatedrubber, capable of forming solutions of -low viscosity, by disaggregatin'g rubber by working on a mill and then chlorinating the disaggregated product. Such dis:

aggregation is open to the objections that the viscosity of the disaggregated; produet is still considerable and higher than desirable. Moreover,- suchdisaggregat-ionrequires much time and results in development of undesirable-color in the chlorinated rubber. It has also been proposed to reduce the viscosity. of the rubber, either raw or previously disaggregated, during the chlorination cycle by introducing an oxygen-containing gas into. the chlorination reac-. tion solution. This procedure leaves much to be desired, however, since it does not reduce the viscosity early enough in the process to gain the advantages of working i with low viscositysolutionsi 'It has also been'propos'ed i to reduce the viscosity of the chlorinated rubber after chlorination is complete by introducinga mixture of-chlorine and an oxygen-containing gas into the chlorinated rubber solution, but this process is uneconomical, time consuming, and not subject to uniform control." Previous proposals to reduce the viscosity of the rubber by oxidation prior to chlorination have not been satisfactory because such methods have resulted in chlorinated prod- "tion viscosity. A stream .intothe resultingrubber-'solutionofreducedtviscosity at a to provide an improved method for'prod ucing chlorinate'dfrubber having great diversity for removing the limitations heretofore existent. Among the objectives accomplished in accordance with this invention are the following:

Provisionof a method for chlorinating rubber which is subject to exact and predetermined control of theviscosity of the final chlorinated rubber produced.

Provision of a method for chlorinating rubber'which substantially eliminatesithe break during chlorination; heretofore encountered,

Provision of a 'methodfor chlorinating rubber which eliminates the necessityfor mechanical disaggregationof the rubber prior to chlorination.

Provision ofa method for 'chlorinatingrubber of greatly improved eificienc'y, whereinirubber solutions of 'subst'an tially higher. solids content are chlorinated in less time than heretofore possible, even with solutions of low solids content, wherein-solvent losses d ring chlorination are substantially-reduced, wher in. mechanical hand-ling.

through pumps, pipes. and" filters. is. greatly] facilitated, and wherein chlorination can be 'ac comp lished 'over' abroad temperature rangeheretoforelargely impractical because of the break or phase "separation encountered.

Provision offza'rrnethod'forchlorinatingrubber which yields a chlorinated product of improved uniformity.:; I

Other-objects-rofrthe invention: Will ppear hereinafter, the novelfeatures: and; 'combinat-ionsbeing: set'fort-lrjin;

the appendedfclaims. 1

Generally des'cr-i'bedythe present" invention COIHPIlSfiSs passing; astreanr of inert: gas -containing-up:-toeabout9%- by weight'ofchlorinedioxide-into a solution of; rubber in a solvent Substantiallyinert to'chlorine'until; the Viscositynof the rubber; solution has been reduced; to aFvalue- 35' less than ab0ut;5%yof the original:rubber-solutionyvisa cosity,-"and thereafterchlorinating the resulting? rubber solution of reduced; 'viscosityat a temperature between" i Y about;-25= C. andabout 7 0 C; withoutjphafsev separation:

during- ClIllOIalIlfitlOIlyllhI-ll chlorinated rubber-having about 66% 'by'we'ight 'of chlorineis produced. 1

In, one cmbodiment'rof the invention-raw crepe r-ubber' is digested and washed in accordance with the digestion and washing'method described in U. S. 2,252,728 and is then dried. The resulting dry, digested rubber is then dissolved in asolvent substantially inert to chlorine, such as carbon tetrachloride, and a stream of inert carrier gas, preferably air, containing fromabout 4% to about 8% of chlorine: dioxide is passed, into therubbersolution until I the viscosity of the rub'bersolution has been reduced to a value less than about 5% of the original rubber soluf chlorine gas (is then passed temperature betweenabout 25= C. an'dabout70" C. until chlorinated rubber-having a'{chlorine "content of about ucts havin'g undesirable characteristics, have in'v'olve'd'ex"' cessive solvent losses, and have not been subject to accurate control.

Heretofore, chlorination of rubber has been characterized by a so-called break orseparation into two" phases during the chlorination; This break actually involves a separation of partially chlorinated rubber from solution. Upon continued chlorination, the chlorinated rubber eventually goes back into solution, but during the. break period the rate of chlorination is greatly reduced. In order to reduce the time during which the 66% is "produced. The chlorinated rubber-is then recovered by precipitationv in-hotwater: and'the solid chlo-- rinated rubber after. washingis'freed frorn 'water 'by draining, centrifuging.and:the--like, and-is then-dried. It is a characteristic of. the'present invention that. chlorination proceeds to completion substantially withoutphase separa- -tion, or a so-calledv break, during chlorination.

The general nature of the inventionha-ving been set forth hereinabove,;the followin'g examplesillustrate some chlorination process isin the break stage, it has been customary to employ quite high temperatures, even up to C. or C., and hence undesirable solvent losses as well as yield losses have been encountered.

Accordingly, it is the principal object of this invention typical and specific embodiments thereof: "However, these are not 'to be'construed as limiting the invention.

Example I Nine hundred'twenty pounds of crepe rubber, after being" digested, Washed andfdriejdinaccordance with the procedure set forthiin Example 2 of U. S. Patent 2,252,728toJohn MerriamPeterson, was then milled for IOminuteson heated; corrugated .rolls. This rubber was then dissolved in carbon tetrachloride to produce a solu- Patented Dec. 16,1958.

tion containing 4.4% by weight of rubber, and having an initial viscosity of 470 seconds at 25 C., as measured by the time for a 20 ml. pipette having the tip cut off to empty (hereinafter referred to as the pipette viscosity).

This rubber solution was brought to a temperature of 31 C. and maintained at this temperature while passing a dry stream of air containing 4.9% by weight of chlorine dioxide into the rubber solution. The chlorine dioxidecontaining gas stream was passed into the solution at a rate equivalent to 1.0 pound of chlorine dioxide per hour until the pipette viscosity of the rubber solution was reduced to 5 seconds, which valueis equal to approximately 1.16% of the original rubber solution viscosity. Chlorine dioxide consumption amounted to 0.64 lb. per 100 lb. of rubber treated.

The chlorine dioxide was generated immediately before use by means of a standard Olin-Mathieson chlorine dioxide generator (Olin-Mathieson Chemical Corporation, 460 Park Avenue, New York, New York). This is a dry type generator in which metered streams of dry air and dry chlorine gas are mixed and then passed through a column of dry sodium chlorite to generate chlorine dioxide. The chlorine is converted substantially quantitatively into chlorine dioxide according to the following equation:

The air is simply an inert carrier gas for the chlorine dioxide.

The resulting rubber solution of reduced viscosity was then charged to a chlorinating vessel and was chlorinated by passing a stream of chlorine gas into the rubber solution while applying cooling water to the jacket of the chlorinating vessel to hold the temperature of the chlorination reaction mixture at about 70 C. or slightly under 70 C. This was necessary in view of the vigorous exothermic character of the chlorination reaction. Chlorination proceeded smoothly and uniformly to completion without phase separation duringchlorination. Chlorination was continued until test indicated completion of the chlorination reaction. This can be readily ascertained by a sharp increase in the chlorine gas content of the off-gas from the chlorination reaction. Another quick control method consists in adding 3 ml. of 98% sulfuric acid and 5 ml. of ethylene bromide to a 3.8 gram sample of the chlorination dope in a x 6 inch test tube and heating the mixture with constant stirring for 5 minutes in a boiling water bath. If chlorination is incomplete, the mixture turns black indicating the presence of unsaturation in the rubber and, therefore, incomplete chlorination. On the other hand, a completely chlorinated rubber contains substantially no unsaturated linkages. Accordingly, when the chlorination dope contains substantially completely chlorinated rubber, the above control test will be negative for unsaturation. The mixture in the test tube separates into two layers, and the bottom layer will at most be only light tan in color.

Upon completion of chlorination, absorbed chlorine and hydrogen chloride in the chlorinated dope were largely removed by distillation, after which the chlorination dope was run into hot water to precipitate the chlorinated rubher. The total chlorination cycle, including time to charge the rubber solution to the chlorinator, actual chlorination time, and time required to distill off absorbed hydrogen chloride and chlorine from the chlorination dope after completion of chlorination was 7.9 hours.

After removal of residual carbon tetrachloride by further treatment of the precipitated product with hot water near the boiling point, and washing the product with water to remove residual acidity, the product was drained and dried.

The resulting product upon analysis was found to contain 66.5% chlorine by weight, and a viscosity of 22 centipoises as measured in a 20% toluene solution at 25 C.

Examples 28 Following substantially the procedure set forth in Example l, a number of runs were made wherein type, prior treatment, and concentration of rubber were varied, wherein concentration of chlorine dioxide and rate of treatment and temperature of treatment with chlorine dioxide were varied. The following table sets forth pertinent data with respect to these variables, together with viscosity data on the treated rubber solutions and data on the chlorinated products obtained. Substantially no phase separation during chlorination was encountered in these runs.

Example Numbers Type of Rubber 1 (a) (c) (b) Ru ber weight, lb 980---- 1,360-. 1,000-- 1,040 1,060 1,220. Rubber concentrationincarbon tetra- 5.2 6.6-.-. 4.9---- .8 5.9.

chloride solution, percent by wt. Temp. of rubber solution during 29---" 34.--" 28 40 61.

chlorine dioxide treatment, C. Original viscosity of rubber solution, 340-.-. 1,250-. 1,900 1,800 3,600 1,700.

pipette viscosity, seconds. Viscosity of rubber solution after 5 1 26.--" 5 0-.-- 20 18 5 13.5

chlorine dioxide treatment, pipette viscosity, seconds. Viscosity of rubber solution after 1 5.--- 2 4---- 0 26--- 1.1 0 51 0.79.

chlorine dioxide treatment as percentage of original viscosity. Chlorine dioxide concentration in 4.7-. 3 8 7.9-.-- 7.2 7.7 7.7 7.3.

inert carrier gas (air) stream, percent by wt. Rate of chlorine dioxide introduction 1.0-.-- 0.81-..- 1.65-.. 1.55 1.04 0.97 0.40.

into rubber solution, pounds per our. Chlorine dioxide consumption, 0.30"- 0.35--- 0.59.-- 0.37 0.29 0.30 0.18.

pounds per pounds of rubber. Total chlorination cycle, hours 7.8--.. 15.6-.. 8.6-.-- 9.5 10.3 9.1 9.6. Degree of chlorination in final cblo- 67.5-.. 66.0--- 66.2- Approx. 67".. Approx. 67.... Approx. 67 Approx. 67.

rinated rubber product, percent by wt. of chlorine. Viscosity of chlorinated rubber, cps. 30.6-.- 57.4--- 28.0 57 22 30 7. Air introduced into chlorination mix None None None 15 lb. per hr. 15 lb. per hr. 15 lb. per hr. 1511b. per hr.

ture during chlorination. for 48 min. for 12 min. for 24 min. for 102 min.

1 (a) Indicates crepe rubber which was digested, washed and dried according to Example 2 of U. S. latcnt 2,252,728, and then milled for 10 minutes on heated, corrugated rolls. (b

) Indicates crepe rubber which was digested, washed and dried according to Example 2 of U. S. Patent 2,252,728, but which received no milling treatment after drying.

I The total chlorination cycle includes time to charge rubber solution to chlorinator, actual chlorination time and time n-quiml to distill oil absorbed hydrogen chloride and chlorine from the chlorination dope after completion of chlorination.

3 Measured on 20% by weight chlorinated rubber solution in toluene at 25 C In Examples 1-8, inclusive, above, .the average weight,

of rubber chlorinated was approximately 1067 lb. The average. overall chlorination cyclein these examples was 9.8 hours. In previous practice, without the benefit of this invention, an average of 825 lb. of rubber could be chlorinated in an average time of 9.9 hours for the overall chlorination cycle. The increase in chlorinator capacity in accordance with this invention Was-therefore,-

approximately 29%, based on prior practice. At the same time, carbon tetrachloride losses were materially lowerv than in prior practice, and handling of the rubber solutions and partially chlorinated rubber dopes in plantequipmentincluding pumps, pipes, filters, chlorination vessels, etc., was greatly facilitatedin comparison to prior art practice. 7

Examples 9 and Raw crepe rubber which had not received any prior digestion or milling treatment was employed in these examples, employing substantially the procedure set forth in Example 1.. Pertinent data on these examples,similar able'inert carrier .gasesifor the purposes of this inven tion include air, nitrogen, waste combustion gases from I heat boilers, neon,.helium,. argon, or any other gas which is substantially inert to chlorine'dioxide under. the conto the data set forth for Examples 28, are presented in the following table. during chlorination was encountered in these examples employing raw crepe rubber having no prior digestion or milling treatment.

Example Numbers Type of Rubber 1 1.

Rubber weight, lb

Rubber concentration in carbon tetrachloride solution, percent by wt.

Temperatureof rubber solution during chlorine dioxide treatment, C.

Originalviscosity of rubber solution,

pipette viscosity, seconds.

Viscosity of rubber solution after chlorine dioxide treatment, pipette viscosity, seconds.

Viscosity of rubber solution after chlo- 0.092 0.52.

rine dioxide treatment as percentage of original viscosity.

Chlorine dioxide concentration in inert 6.4 to 7.7 8.1.

carrier gas (air) stream, percent by wt.

Rate of chlorine dioxide introduction 0.902 a. 0.94,

into rubber solution, pounds per hr.

Chlorine dioxide consumption, pounds 0.28 0.17.

per 100 pounds of rubber.

Total chlorination cycle, hrs 2 9.68 9.17.

Degree of chlorination in final chlori- 66.1 Approx. 67.

nated rubber product, percent by Wt. of chlorine. Viscosity of chlorinated rubber, eps. 5 Air introduced into chlorination mixlb. per hr. ture during chlorination. for 320 min.

887. None.

(a) Indicates raw crepe rubber which had not received any prior digestion or milling treatment. v

2 lhe total chlorination cycle includes time to charge rubber solution Substantially no phase separation to chlorinator, actual chlorination time, and time required to distill off absorbed hydrogen chloride and chlorine from the chlorination dope after completion of chlorination.

3 Measured on 20% by weight chlorinated rubber solution in toluene at 25 C.

It is important to point out that without chlorine dioxide treatment to reduce rubber viscosity in the manner contemplated by this invention, it becomes economically impractical to employ raw crepe rubber because of the extremely low solids concentration which could be handled through the chlorination process.

An important and necessary feature of this invention involves passing a stream of inert gas containing up to 9% by weight of chlorine dioxide into a solution of rubber in asolvent substantially inert to chlorine until the viscosity of the rubber solution has been reduced to a value less than about 5% of the original rubber solution viscosity.

Ordinarily, it is preferred to stir the rubber solution vigorously while bubbling the gas stream containing the chlorine dioxide into the solution, and it has been found that the amount of reduction of rubber viscosity is directly proportional to the amount of chlorine dioxide which has been added to the rubber solution when all other factors are held constant. Because of this fact, it is possible to calculate and predetermine with accuracy the 6 amount of. chlorine=dioxide necessary to. produce a chlorinated rubber product .of any desired-viscosity.

Since chlorinerdioxide-in high concentrations is exf plosiye, it is necessary. to generate the chlorine dioxide and entrainit immediately with av large excess of: an

inert carrier gas. A very convenientmethodlfor generating chlorine dioxide-islset forthrinExample' 1. Suit-' ditions employedain practicingrthis invention... Air is the preferred incrtcarrier gas.

Theexplosivenature of .chlorine 'dioxide.inrconcem trations of about 14% by weight and above limitsztheper hour on .the'basis ofa charge of approximately 1000- lb. of rubber.v .However, .fromthe 'standpointof operability in: this invention,thereais no limitation on the rate of introduction. of chlorine'dioxide into the rubber solu- 1 tion. For practicalreasons;howcver,'it.is not advisable.

to employivery low rates. because. of. the excessive time involved,2or;excessivelyt high :rates .because of the possibility of lossesxofchlorin: dioxide due to absorption inetliciencies. :-'A practical: operating range .is between about 0.4 and about'l 65 lb. per hour-based on a. 1000 n lb. charge of rubber.

Any rubber :Whichcan bedissolved ina solvent substantially inertlto chlorine is suitable in practicing this invention. Thus, by Way of example,*the rubber employedcan be crude crepe rubber or: smoked sheetrub: 1 her, as they appear on the. market, or? either :of .these,.as

Well as cheap low grades of rubber, which have been given a. purifying. digestionand washing.:treatment :to remove various natural impurities, as well as various. syntheticrubbers. If desired, the rubber can be given a hot milling treatment to efiect a partialbreakdown of rubber viscosity prior to dissolving the rubber in solvent. H However, it is presently preferred .to employ a purified" rubber such as crepe rubber which has been given a digestion and washing treatment to remove natural impurities, and is then dried, but which has not been given a milling treatment on hot rolls after drying to disaggregate the rubber. Suitable digestion methods are disclosed in U. S. Patents 2,252,728, 2,401,133, and 2,401,194.

Prior to treatment with chlorine dioxide, the rubber is dissolved by any suitable means in a solvent which lS- Suitable solvents in-- clude, by way of example, carbon .tetrachloridegtetrasubstanftially inert to chlorine.

chloroethane, ethylene dichloride, chloroform, and the like. Carbon tetrachloride is the preferredsolvent for the purposes of this invention.

The preferredconcentration of rubber in solution is However,

between about 4% and about 8% by weight. for some purposes, solutions containing appreciably more -than 8% by weight .of rubber can be employed, if de sired. The-limiting factor controlling the upper amount of rubber which can be employed is the ability to stir the solution, and with present equipment this upper limit is approximately 15% by weight.

relation to the amount of solventinvolved.-

Rubber concentrations below 4% by weight are operative, but not economical because of the small amount of rubber being treated in- From the standpoint of operability in this invention, there is no limitation on the temperature of the rubber solution into which chlorine dioxide is introduced, for chlorine dioxide is effective in reducing the viscosity of the rubber solution at any temperature. However, temperatures above about 65 C. are not advisable because the rubber solvent employed is volatilized at an excessive rate. Low temperatures, below ordinary room temperatures, are likewise not advisable because at such temperatures reaction rate of chlorine dioxide with rubber is slow and rubber solution viscosities become excessively high. A practical operating range is between about 25 C. and about 65 C. For optimum results, a temperature between about 30 C. and about 65 C. is preferred.

It is important and necessary to reduce the viscosity of the rubber solution to a value less than about of the original rubber solution viscosity with chlorine dioxide, in order to subsequently chlorinatethe rubber in solution without encountering a break or phase separation during chlorination. The course of viscosity reduction can be readily followed by means of the pipette viscosity method set forth in Example 1. For most purposes, it is preferred to reduce the rubber solution viscosity to a value less than about 2.5% of the original rubber solution viscosity.

Chlorination of the rubber solution of reduced viscosity in accordance with this invention is conducted at temperatures between about 25 C. and about 70 0. without a break or phase separation during chlorination. For optimum results it is preferred to conduct the chlorination at a temperature between about 60 C. and about 70 C. This makes possible a rapid, uniform chlorination with minimum solvent losses. If desired, chlorination may be conducted in the presence of ultraviolet light, but this is not necessary. In all other respects, chlorination follows customary prior art practice, and is continued until control tests, as set forth in Example 1, indicate that chlorinated rubber of about 66% chlorine by weight has been produced. Recovery, washing, bleaching, stabilization and drying of the chlorinated rubber product follow customary prior art practice, and,

therefore, do not require detailed discussion in this specification.

From the foregoing description, it will be apparent that the advantages of the invention are multifold. The principal advantage resides in the attainment of the objectives as hereinbefore set forth in providing a novel and improved method for chlorinating rubber which overcome important disadvantages of the prior art.

What we claim and desire to protect by Letters Patent 1. The process for producing chlorinated rubber which comprises passing a stream of inert gas containing chlorine dioxide in an amount up to about 9% by weight in a stirrable solution of rubber containing up to about 15% by Weight of said rubber in a volatile chlorinated aliphatic hydrocarbon solvent substantially inert to chlorine until the viscosity of the rubber solution has been reduced to a value less than about 5% of theoriginal rubber solution viscosity, and subsequently chlorinating the resulting rubber solution of reduced viscosity at a temperature between about 25 C. and about 70 C. without phase separation during chlorination until chlorinated rubber having about 66% by weight of chlorine is produced.

2. The process of producing chlorinated rubber which comprises passing a stream of air containing from about 4% to about 8% by weight of chlorine dioxide into a stirrable solution of rubber containing up to about 15% by weight of said rubber in a volatile chlorinated aliphatic hydrocarbon solvent substantially inert to chlorine until the viscosity of the rubber solution has been reduced to a value less than about 5% of the original rubber solution viscosity, and subsequently chlorinating the resulting 8 rubber solution of reduced viscosity at a temperature between about 25 C. and about 70 C. without phase separation during chlorination until chlorinated rubber having about 66% by weigh of chlorine is produced.

3. The process of producing chlorinated rubber which comprises passing a stream of air containing from about 4% to about 8% by weight of chlorine dioxide into a stirrable solution of rubber containing up to about 15% by weight of said rubber in a volatile chlorinated aliphatic hydrocarbon solvent substantially inert to chlorine at a temperature between about 25 C. and C. until the viscosity of the rubber solution has been reduced to a value less than about 5% of the original rubber solution viscosity, and subsequently chlorinating the resulting rubber solution of reduced viscosity at a temperature between about 25 C. and about C. without phase separation during chlorination until chlorinated rubber having about 66% by weight of chlorine is produced.

4. The process of producing chlorinated rubber which comprises passing a stream of air containing from about 4% to about 8% by weight of chlorine dioxide into a stirrable solution of raw crepe rubber containing up to about 15% by weight of said rubber in carbon tetrachloride at a temperature between about 25 C. and about 65 C. until the viscosity of the rubber solution has been reduced to a value less than about 5% of the original rubber solution viscosity, and subsequently chlorinating the resulting rubber solution of reduced viscosity at a temperature between about 25 C. and about 70 C. without phase separation during chlorination until chlorinated rubber having about 66% by weight of chlorine is produced.

5. The process of producing chlorinated rubber which comprises passing a stream of air containing from about 4% to about 8% by weight of chlorine dioxide into a stirrable solution of rubber, digested and washed to remove natural impurities, containing up to about 15% by weight of said rubber in carbon tetrachloride at a temperature between about 25 C. and about 65 C. until the viscosity of the rubber solution has been reduced to a value less than about 5% of the original rubber solution viscosity, and subsequently chlorinating the resulting rubber solution of reduced viscosity at a temperature between about 25 C. and about 70 C. without phase separation during chlorination until chlorinated rubber having about 66% chlorine by weight is produced.

6. The process of producing chlorinated rubber which comprises passing a stream of air containing from about 4% to about 8% by weight of chlorine dioxide into a solution containing from about 4% to about 8% of rubber, digested and washed to remove natural impurities, in carbon tetrachloride at a temperature between about 25 C. and about 65 C. until the viscosity of the rubber solution has been reduced to a value less than about 5% of the original rubber solution viscosity, and subsequently chlorinating the resulting rubber solution of reduced viscosity at a temperature between about 25 C. and about 70 C. without phase separation during chlorination until chlorinated rubber having about 66% chlorine by weight is produced.

0 References Cited in the file of this patent UNITED STATES PATENTS 1,826,275 Dyche-Teague Oct. 6, 1931 2,020,076 Mollney Nov. 5, 1935 2,037,599 Schweitzer Apr. 14, 1936 2,140,715 Peterson Dec. 20, 1938 FOREIGN PATENTS 671,499 Great Britain May 7, 1952 685,020 Great Britain Dec. 31, 1952 OTHER REFERENCES Mellor: Comprehensive Treatise on Inorganic Chemistry, vol. II, Longmans, Green and Co., 1922, page 288. 

1. THE PROCESS FOR PRODUCING CHLORINATED RUBBER WHICH COMPRISES PASSING A STREAM OF INERT GAS CONTAINING CHLORINE DIOXIDE IN AN AMOUNT UP TO ABOUT 9% BY WEIGHT IN A STIRRBLE SOLUTION OF RUBBER CONTAINING UO TO ABOUT 15% BY WEIGHT OF SAID RUBBER IN A VOLATILE CHLORINATED ALIPHATIC BYDROCARBON SOLVENT SUBSTANTIALLY INERT TO CHLORINE UNTIL THE VISCOSITY OF THE RUBBER SOLUTION HAS BEEN REDUCED TO A VALUE LESS THAN ABOUT 5% THE ORIGINA RUBBER SOLUTION VISCOSITY, AND SUBSEQUENTLY CHLORINATING THE RESULTING RUBBER SOLUTION OF REDUCED VISCOSITY AT A TEMPERATURE BETWEEN ABOUT 25*C. AND ABOUT 70*C. WITHOUT PHASE SEPARATION DURING CHLORINATION UNTIL CHLORINATED RUBBER HAVING ABOUT 66% BY WEIGHT OF CHLORINE IS PRODUCED. 